Bushings are used for a variety of purposes, and typically, a bushing is a hollow cylindrical component, such as a tube or sleeve, that may be used as a guide or spacer for various tools, fasteners, parts, etc. In some applications, a bushing may form a portion of a bearing assembly.
In the aerospace industry, one application for bushings includes ensuring that components that extend through the wall of a fuel tank are sufficiently and electrically grounded to the wall of the fuel tank, so as to avoid sparking. In modern aircraft construction, in which airframes, including fuel tanks, are constructed of carbon fiber reinforced polymers, and when utilizing existing bushing technology, the holes that extend through the wall of a fuel tank and the bushings themselves that are press-fit into the holes are required to have very tight tolerances with respect to each other to ensure proper engagement between, and thus grounding of, the bushings and the wall of the fuel tank.
The manufacturing costs associated with these tolerances are not insignificant.